The block copolymer refers to a polymer consisting of a chain where monomers A are repeatedly connected and a chain where monomers B are repeatedly connected, as described in Non-Patent Document 1, p. 90 and 91. A chain consisting of the monomers A or the monomers B is called a block chain. Furthermore, a diblock copolymer formed of a single block chain A and a single block chain B is expressed by A-b-B. In the present invention, a block chain having a slightly branched portion may not be excluded.
The block copolymer forms an ordered microdomain structure, when constituent blocks are immiscible and hence separated into phases. Such an aggregate is called a microphase-separated structure.
The microdomain structure shows various types of morphology depending upon the composition of the block copolymer. The morphologies are classified into, for example, a lamellar structure in which two block chains are alternately layered; a cylindrical structure in which one of the block chains form cylinders in the matrix formed of the other block chain; a spherical in which one of the block chains form spheres in the matrix formed of the other block chain; and a network structure called a gyroid structure.
However, these microdomains cannot be enlarged beyond the stretch of block chain components thereof. Usually an orderly oriented texture structure (hereinafter, referred to as a “grain”) is formed only within a narrow range of a sub-micron size. Also, when a plurality of grains are aggregated, a microphase-separated structure non-orderly oriented is formed. Namely, the microphase-separated structure has macroscopically a random orientation and forms an isotropic structure as a whole. Therefore, it is difficult to effectively use it as a functional material based on the characteristic of a microphase-separated structure orderly oriented. This is a problem.
To solve this problem, Non-Patent Document 2 discloses a structure having a uniform orientation in the in-plane direction. This is formed, for the first time, by purposely placing a layer on the surface of which a pattern is formed in advance, under a block copolymer.
However, to form a pattern in the surface of the underling layer, it is necessary to use nanofabrication techniques such as photolithography or use of a probe tip of a scanning probe microscope. Therefore, as the size of pattern is reduced more and more, a more complicated step must be performed for a long time by use of expensive equipment. Besides this, the material of a substrate to be processed and the shape and area thereof are also limited. In addition, the formed microphase-separated structure does not have temperature response at all.
Furthermore, Patent Document 1 discloses a lamellar structure, which is formed by placing a block copolymer on a substrate having a predetermined surface roughness and annealing it. Also Non-Patent Documents 3 and 4 disclose a lamellar structure, which is formed while orientation is controlled by epitaxial growth.
However, in the method disclosed in Patent Document 1, the substrate must be processed in advance and an annealing step is required. In this respect, this method is far from a convenient method. Even if the method disclosed in Non-Patent Document 2 is used, it is estimated that a visible-size single crystalline giant grain is not easily formed. In addition, no discussion is made on the temperature dependence of the obtained lamellar structure.
On the other hand, with respect to the structural color due to Bragg reflection depending upon periodical microphase-separated structure of a high-molecular weight block copolymer, only a few studies are known which are made in an equilibrium system using a good solvent, as disclosed in Non-Patent Document 5. However, with respect to temperature dependence, it has only been generally reported that the wavelength of a structural color gradually changes (power law of −⅓ power) depending upon temperature.
Also, with respect to a method of immobilizing a microphase-separated structure, Non-Patent Documents 6 and 7 disclose a method of forming a thin film by evaporation of a solvent. However, since distortion occurs by evaporation of a solvent during a film formation process, nothing is obtained other than a distorted microphase-separated structure.
A case where a microphase-separated structure of a block copolymer is used as a laser resonator is described in Patent Document 2. The microphase-separated structure to be used as a laser resonator is formed by the solution cast method. However, no discussion was made on a temperature dependence of period of a microphase-separated structure, that is, cavity length determining oscillation wavelength.
A case where a colloid crystal is used as a photonic crystal serving as a laser resonator is described in Patent Document 3 in the same as in the previous paragraph. However, the photonic crystal using a colloid crystal is used only as an output reflecting mirror and a luminescent layer is separately provided. Therefore, different from the structure of the present invention where a luminescent layer containing laser medium is embedded into a laser resonator, that is, laser medium is uniformly introduced into microphase-separated structure (the resonator), optical parallelism of the luminescent layer and the output reflecting mirror must be controlled. In addition, similarly to Patent Document 2, no discussion is made on temperature dependence as a characteristic of a resonator. A mention is only made of an advantage, that is, high thermal stability.    Patent Document 1: Japanese Patent Application Laid-Open No. 2004-99667    Patent Document 2: Japanese Patent No. 3507659    Patent Document 3: Japanese Patent Application Laid-Open No. 2006-287024    Non-Patent Document 1: Norio Ise et al., “New Polymer Chemistry Introduction” Kagaku-dojin Publishing Company, Inc, 1995    Non-Patent Document 2: L. Rockford et al. Physical Review Letters 82, 2602 (1999)    Non-Patent Document 3: Sang Ouk Kim et al., Nature, Vol. 424, p. 411 to 414 (2003)    Non-Patent Document 4: Richard A. Register et al., Nature, Vol. 424, p. 378 to 379 (2003)    Non-Patent Document 5: Mitsuhiro Shibayama et al., Macromolecules, 16, p. 16 to 28 (1983)    Non-Patent Document 6: Michael R, Bockstaller et al., J. Phys. Chem. B, vol. 107, No. 37, p. 10017 to 10024 (2003)    Non-Patent Document 7: Tao Deng et al., Polymer, No. 44, p. 6549 to 6553 (2003)